High-Resolution Simulation of a Violent Tornado in the 27 April 2011 Outbreak Environment

A recent study by Orf et al. (2017) presented an overview of a very high-resolution numerical simulation of a long-lived EF5 tornado embedded within a parent supercell based on initial conditions from a proximity sounding from the 24 May 2011 El Reno, OK tornado. Several salient features were identified in the simulation: (a) a streamwise vorticity current (SVC) situated along the supercell forward-flank downdraft boundary (FFDB) that appeared to be a critically important structure influencing tornado development, intensification and maintenance, (b) a vertical vorticity sheet (VVS) along the storm’s FFDB that hosted numerous developing vortices, the most prominent being cyclonic, which strongly influenced tornadogenesis and continued to impact the tornado through much of its life, and (c) sporadic downdraft surges occurring in the rear flank of the storm. Given the important role the SVC and VVS play in the 24 May 2011 simulation, a crucial question is whether these features are major factors in other supercells that produce long-lived violent tornadoes.

We will present preliminary results from a high-resolution simulation initialized with a sounding from the 27 April 2011 tornado outbreak environment in which the simulated supercell produced a violent long-track tornado. Preliminary results indicate that the features described above in the 24 May simulation are also present in 27 April simulation, although there are differences in their structure and evolution. Like the 24 May simulation, tornadogenesis commenced through a vorticity accumulation process via vortex coalescence under a strengthening updraft associated with the lowering base of the deep-storm mesocyclone. However, the rear-flank downdraft and leading-edge gust front appear to play a more prominent role in the 27 April case. In addition to a comprehensive overview of the evolution of the 27 April supercell and associated violent tornado via advanced visualization, the presentation will compare tornadogenesis and maintenance processes between the 24 May and 27 April cases.

References:

Orf, L., R. Wilhelmson, B. Lee, C. Finley, and A. Houston, 2017: Evolution of a long-track violent tornado within a simulated supercell. Bull. Amer. Meteor. Soc., 98, 45–68, https://doi.org/10.1175/BAMS-D-15-00073.1.